Sump pits or wet wells are known and used in many industries to collect fluids at a site. A pump inlet is conventionally placed at the bottom of the sump pit or wet well to pump the fluids out of the sump pit or wet well. Many arrangements have been devised for facilitating the accumulation of fluids in a sump or wet well, and for pumping the fluids out of the sump or wet well.
Some arrangements comprise a tank into which a pump is lowered to pump fluids from the bottom of the tank. Other arrangements, which are particularly relevant to this disclosure, comprise the use or formation of a prerotation basin within a sump pit or wet well.
Prerotation basins are essentially comprised of a basin having an upper edge, which provides a weir, an internal bowl-like configuration into which a pump inlet is positioned, and a vertically-oriented entry slot formed generally along the side of the basin, at a tangential angle typically, to direct fluid into the internal bowl-like configuration. Fluid entering the bowl-like configuration through the slot is directed at an angle which causes the fluid to “prerotate” in the direction of rotation of the pump impeller, thus facilitating efficient fluid uptake.
The fundamental principle by which prerotation basins function is the establishment of an elevation difference between the liquid within the prerotation basin and liquid outside the prerotation basin. This is achieved by configuring the basin arrangement so that the entrance to the slot from the sump or wet well is at a higher elevation than the bottom of the bowl-like interior of the basin. That is, the entry point of the slot is placed at a higher elevation than the bottom of the interior of the prerotation basin to provide a downwardly sloping channel, which causes increased energy to be imparted to the fluid entering into the basin, thereby creating rotation of the fluid.
Notably, in conventional prerotation basin arrangements, the elevation differential is further achieved by the installation of the prerotation basin in the sump pit or wet well. That is, prerotation basins are provided in the bottom of the sump or wet well either by positioning a suitably shaped mold in the sump or wet well and pouring concrete about the mold to form the basin or, more typically, by placing a pre-cast three-dimensional basin form into the bottom of the sump or wet well and pouring concrete about the pre-cast form to complete the installation. In either case, concrete is poured into the sump pit or wet well to the level of the entry point of the slot. The required depth to which the prerotation basin must be set into place with concrete represents a very significant aspect of the cost of prerotation basin installation due to the amount of concrete required. Further, the addition of concrete to the sump pit or wet well also reduces the volume of water that the sump pit is capable of holding, which in turn requires more frequent on and off cycling of the pump that is installed in the sump pit.
In many industries, the fluid that is being pumped out of the sump pit or wet well contains solids, some of which tend to float to the top of the fluid, and others which are neutral and/or sinking. It is important that the solids be pumped out of the pit because solids that are not entrained in the fluid accumulate over time and eventually clog the basin, and may result in pumping inefficiencies or pump stoppage. Accumulated solids begin to become malodorous and may be toxic. Consequently, when solids accumulate to an unacceptable level, it is necessary to pull the pump from the basin and send workers into the basin to manually clean the solids from the basin. The manual removal of solids is costly and can be dangerous to the workers.